The present invention relates to a ball valve with a builtin check valve, employed in piping for transmitting a fluid such as water, oil, gas or the like, and especially, for use in piping in which the fluid is to be prevented from flowing backward.
In conventional piping for preventing a counter flow of a fluid, it has been ordinarily adopted to mount both a check valve (such as swing check valves, lift check valves, and the like) and a shutoff valve (such as gate valve, globe valves, ball valves, butterfly valves, and the like) in parallel. However, this suffers the drawbacks of high material cost and high assembly cost and requires a large exclusive space for mounting the two different valves in parallel. These are the drawbacks inherent in the conventional piping.
In view of this, there has been proposed a globe stop-end check valve which is a combination globe valve and lift check valve. This globe stop-end check valve is classified into two groups, one of which is employed in a horizontal portion of the piping and the other of which is employed in a bent portion between the horizontal portion and a vertical portion of the epiping. In other words, there is no such globe stop-end check valve which is employed in the vertical portion of the piping. In addition to this drawback, the globe stop-end check valve suffers from its large fluid resistance and a rattling noise produced when it has checked a counter flow of a fluid.
There has also been proposed a ball valve provided therein with a ball having a through hole with a built-in check valve in the through hole. In the ball valve of this type, since the direction in which a fluid flows is invariable it is necessary to always recognize the direction, and since a valve handle is often detached from and attached to a valve stem during mounting and maintenance work of the ball valve, it is necessary that the handle can easily be attached to and detached from the stem with exactitude. In the prior art ball valve, however, the stem has its upper portion formed with a pair of flat outer surfaces, and the handle has a fitting hole provided with a pair of flat inner surfaces snugly fitted on the flat outer surfaces of the stem. That is to say, the handle is mounted on the stem by a snug fitting between the pair of inner flat surfaces of the former and the pair of outer flat surfaces of the latter. In the maintenance work, for example, the mounted handle is once detached from the stem and is then attached to the stem again. In this case, if the pair of inner flat surfaces of the handle should be fitted inversely on the pair of outer flat surfaces of the stem, then the check valve will malfunction. Such inconvenience has heretofore been often encountered. Furthermore, since the conventional ball valve is not provided with any means for confirming whether the ball valve is opened or closed during the mounting or maintenance work of the ball valve, even when the valve handle is correctly mounted on the stem, it cannot be confirmed whether the ball valve is in its opening or closing condition. This leads to a fair possibility of the fluid being permitted to pass through the ball valve by mistake.